1. Field of the Invention
The present invention relates to an adapter for amplifiers in optical lines of the type comprising at least an optical line transmitting apparatus provided with a laser, and an optical line receiving apparatus between which the corresponding optical line amplifiers are interposed.
2. Description of the Prior Art
It is known in the field of optical fiber telecommunication lines that it is very difficult to insert in the line optical amplifiers the parameters of which are compatible with the respective optical parameters of the optical line transmitters and receivers.
This results from the fact that the characteristics required of the optical line amplifier, that is, transmission speed, wavelength and variation of the latter depending upon the working temperature, are different from those normally used by common optical line transmitting and receiving apparatus.
More specifically, it would normally be necessary each time to design a particular circuit configuration, adapted to the parameters of the optical line amplifier and specific to the transmission speed of that line. In terms of operation, this means that it is necessary to make an electrical circuit board in which the related parameters have been adjusted depending upon the specific transmission speed.
In addition, the wavelength control circuits, depending upon the specific temperature which is related to that optical line amplifier, should also be on the same board.
Moreover, difficulties arise in carrying out the electrical connection to said electrical boards present in the transmitter and in the receiver, of the corresponding conversion circuit section arranged in the optical amplifiers, when a given transmission speed threshold equal to 565 megabits is exceeded.
These types of problems, as regards the laser providing the output of the optical transmitter and the corresponding input of the optical receiver related to the receiving apparatus, also give rise to a series of further restrictions due to the fact that the circuitry currently used in transmitting and receiving apparatus does not provide a circuit connection of the analog type for the service channels coupled to the same optical line.
In short, while in known and in currently experimental embodiments, a circuit compactness criterion has been developed in order to limit the number of components and make the interfacing boards mounted at the transmitting and receiving apparatus of the optical fiber lines reliable, it is obvious that, when optical line amplifiers have to be connected in the line, said amplifiers are structurally incompatible with the circuitry normally present in the corresponding optical transmitting and receiving apparatus, due to their operating parameters.
That is to say, when normal transmitting/receiving apparatus is used, the signal on the optical line undergoes alterations greatly modifying the nature of the signal itself in the presence of optical amplifiers.
These restrictions represented by the above-mentioned parameters also constrain one to adopt a variety of circuit solutions, each of them being exclusively limited to the selected operating parameters for that line and meeting the requirements of the optical line amplifiers present on the line itself.
This is mainly due to the peculiarity of the optical line amplifiers which must work within given wavelength ranges, within given wavelength variation limits depending upon temperature, and for any value of the transmission speed.
In fact, as a result of the foregoing, normal optical line receivers have problems with frequency response when they are coupled to optical amplifiers in optical fiber lines.
Taking into account only this series of difficulties due to the parametric restrictions and to the problems concerned with the electrical connections between the optical detector and the related circuitry of the optical line apparatus, attempts have been first made to accomplish a number of solutions each offering predetermined parameters.
It appears obvious, however, that this method is very intensive as regards planning, very expensive and disadvantageous from an industrial point of view.